[Wavytone]

Wikipedia is often useful but it is not a definitive, authoritative source. From my optics texts, to be called "apochromatic" a lens group must be corrected for spherical aberration at two wavelengths or colors and for chromatic aberration at three wavelengths.

Comments:

Reflecting telescopes are inherently apochromatic.

A two-element lens can meet the condition using either fluorite or ED glass, as can many designs with 3 or more elements.

A "lens group" means any number of elements in close proximity ie cemented or airspaced. While the Petzval design can be effectively as good, technically it doesn't meet the definition as it has two groups - a positive objective, and a second group midway to the focal plane. It doesn't take Einstein to add more groups, that's an easy way to find a solution but at the expense of net light loss, scattering and internal reflections, not to mention increased manufacturing cost.